Quantitative detection of hydrogen peroxide in solution above a Streptococcus gordonii (Sg) bacterial biofilm was studied in real time by scanning electrochemical microscopy (SECM). The concentration of hydrogen peroxide was determined to be 0.7 mM to 1.6 mM in the presence of 10 mM glucose over a period of 2 to 8 h. The hydrogen peroxide production measured was higher near the biofilm surface in comparison to Sg grown planktonically. Differential hydrogen peroxide production was observed both by fluorometric as well as by SECM measurements. The interaction between two different species in a bacterial biofilm of Sg and Aggregatibacter actinomycetemcomitans (Aa) in terms of hydrogen peroxide production was also studied by SECM. One-directional y-scan SECM measurements showed the unique spatial mapping of hydrogen peroxide concentration across a mixed species biofilm and revealed that hydrogen peroxide concentration varies greatly dependent upon local species composition.real-time (detection) | metabolite efflux | local concentration | oral flora | Au UME S treptococcus gordonii (Sg) is a member of the viridans group streptococci-Gram-positive oral microbes that are known to ferment sugars into lactic acid and produce hydrogen peroxide in the presence of oxygen (1). The presence of these beneficial oral streptococci has been shown to improve oral health, by either competition with pathogens for nutrients in the oral cavity or by the production of inhibitory concentrations of hydrogen peroxide. Populations of viridans group streptococci negatively correlate with the presence of many notable oral pathogens (2, 3). However, recent work has demonstrated that in vitro Sg can grow in coculture with the opportunistic oral pathogen Aggregatibacter actinomycetemcomitans (Aa) (4). In co-culture Aa preferentially utilizes Sg-produced lactic acid (5) and detoxifies Sg-produced hydrogen peroxide using the KatA enzyme (6). Recent work has demonstrated that hydrogen peroxide induces katA expression as well as apiA, which encodes an immunoprotective factor that renders Aa more resistant to killing by host innate immunity (5). These studies demonstrated induction of gene expression in mixed species biofilms by Sg-produced hydrogen peroxide. Because hydrogen peroxide is rapidly degraded by catalase and can also react with other biological materials, we sought to quantify local hydrogen peroxide concentrations in real time to be utilized for future polymicrobial experiments between Sg, Aa, and other oral bacteria.Previous measurements of hydrogen peroxide have been performed using fluorescence, spectroscopy and other methods (1, 7-10). However, current techniques lack the ability to quantify local hydrogen peroxide concentrations at the surface of a biofilm. In this study, scanning electrochemical microscopy (SECM) was used to address this problem. SECM has the unique ability to set the exact distance from a sensing tip [an ultramicroelectrode (UME) of size ∼10 to 25 μm diameter] to a substrate through a feedback approach curve (11)...

No abstract

No abstract

No abstract

A facile carbon radical reaction procedure and a chemical reduction method were proposed to synthesize Ag nanoparticles on functionalized graphene with uniform, high dispersion and excellent stability. The resultant material showed excellent electrocatalytic activity to nitroaromatic compounds and high sensitivity to the detection of nitroaromatic compounds.

No abstract

The electrochemical behavior of hydroquinone (HQ) was studied by cyclic voltammetry at a glassy carbon electrode (GCE) modified by a gel containing multi-walled carbon nanotubes (MWNTs) and room temperature ionic liquid (RTIL) of 1-butyl-3-methylimidazolium hexafluorophosphate (BMIMPF(6)). At the modified electrode, HQ showed a pair of quasi-reversible redox peaks. The cathodic peak current value (I(pc)) of HQ was 9.608 x 10(-4)A, which is 43 times larger than the one at the GCE, and 11 times larger than that of I(pc) at the MWNTs/GCE. Furthermore, the capabilities of electron transfer on these three electrodes were also investigated by electrochemical impedance spectroscopy (EIS), and the similar conclusion as cyclic voltammetry has drawn. Besides, we also characterized the surface morphology of the prepared composite film using the scanning electronic microscopy (SEM). The MWNTs were pulled away from the tangle in RTIL. The solvent effect of RTIL may be the reason of higher adsorption amount.

No abstract